wget https://cloud-images.ubuntu.com/bionic/current/bionic-server-cloudimg-amd64.img
sudo modprobe nbd max_part=1
sudo qemu-nbd –connect=/dev/nbd0 bionic-server-cloudimg-amd64.img
sudo mount /dev/nbd0p1 /mnt/nbd/ -o noatime
pushd /mnt/nbd
sudo mount -t proc proc proc
sudo mount -t sysfs sysfs sys
sudo mount -t devtmpfs devtmpfs dev
sudo mkdir -p dev/pts dev/shm
sudo mount -t devpts devpts dev/pts
sudo mount -t tmpfs shmtmpfs dev/shm
sudo mount -t tmpfs runtmpfs run
sudo touch run/utmp
sudo mkdir run/lock run/resolvconf
sudo chown root:uucp run/lock && sudo chmod 775 run/lock
sudo ln -s /dev/shm /run/shm
sudo mv etc/resolv.conf etc/resolv.conf.baseimage-backup
sudo cp /etc/resolv.conf etc/
cd ..
sudo chroot /mnt/nbd /bin/bash
<do your thing and exit>
umount nbd
umount -l /mnt/nbd
umount -d -f /mnt/nbd
nbd-client -d /dev/nbd0